where \(\delta \)  is a sufficiently small positive constant. The constraint “\(||\mathbf {q}_m||_2\ll \delta ||\mathbf {w}_m||_2\) " is added to restrict \(\mathbf {q}_m\)  to be around the origin (source), as placing the RIS close to the source leads to the almost sure use of full-array RIS architecture \(\left(\bar{N}=N\right)\) , which maximizes the minimum SNR [1]} and therefore leads to smaller \(\sum _{m\in \mathbb {M}}P_m\) . Fortunately, we can find a practical solution for the problem, as stated in Theorem REF .
